Process of producing grinding bodies



Jan. 8, 1935. 'r. POHL ET AL PROCESS OF PRODUCING GRINDING BODIES Filed Feb. 21, 1953 neoaor' P0111 and JoseSclznez'aez? QM M Patented Jan. 8, 1935 raocass or :raonocmo GRINDING BODIES Theodor Pohl, Frankfort-on-the-Main, and Josef Schneider, Oberursel-on-the-Taunus,

Ger.-

many, assignors to Deutsche Goldund Silber- Scheideanstalt vormals Roessler, Frankfort-onthe-Main, Germany, a corporation of Germany Application February 21, 1933, Serial No. 658,568 In Germany February 26, 1931 6 Claims.

In my co-pending application Serial No. 594,304

'filed on February 20, 1932 there are described grinding bodies, in particular grinding discs of cellular structure, which are uniformly interspersed by artificially produced hollow spaces, the size of which amounts at least to the size of the abrasive grains present, and in some cases may amount to several times the size of the abrasive grains. The hollow spaces which, for example, may be blister-shaped or spherical preferably have the same or approximately the same size and shape. The walls consisting of grinding grains and binding agent which separate the hollow spaces from one another may be porous or non-porous; in some cases also the hollow spaces may be in connection one with another by means of openings.

As the result of further experiments it has been found that it is advantageous to manufacture grinding bodies of the aforesaid kind in such a way that the volume occupied by the hollow spaces and pores is at least 50% of the total volume. preferably 60 to 80% of the total volume.

Such grinding bodies have the advantages that, owing to the large volume of the hollow spaces, they are relatively very light and that, owing to the preponderance of the hollow spaces uniformly distributed throughout the grinding body, they give rise to no undesirable heating up of the tool or of the grinding disc, and that, owing to the formation of a. large number of thin cutting edges at the working surface, they have an excellent grinding action, and, finally, they exhibit great resistance to the stresses occurring when the grinding disc is rapidly rotated.

The manufacture of the grinding bodies may take place in accordance with the process described in the aforesaid co-pending specification. Processes which enable the number and size of the hollow spaces interspersed throughout the grinding body to be regulated have proved to be particularly suitable.

It has been found that excellent grinding bodies of cellular or honeycombed structure, which are uniformly interspersed with apertures of the same or approximately the same size in such a way that in the finished disc the total volume of the hollow spaces exceeds or in some cases considerably exceeds the total volume of the solid mass, can be manufactured by incorporating in the mixture of abrasive material and binding medium substances which are capable of producing gas bubbles in the mass before it solidifies, owing to the action of the paste producing medium, for example water or other substances. Particularly good results have been obtained by employing additional substances of this nature containing active oxygen, such as for example hydrogen peroxide and similar compounds.

The employment of such compounds has the advantage that the oxygen is not given ofi turbulently but it is only given off by the action of certain substances, for example so-called decomposition catalysts. It is, therefore, possible, by varying the amount of hydrogen peroxide employed, by suitably selecting the substance which effects or promotes the evolution of oxygen and by varying the proportions of hydrogen peroxide and the additional substance, to regulate the evolution of oxygen in such a manner that in the finished grinding body the total volume of the hollow spaces exceeds the total volume of the solid (pore-free) mass to the desired extent.

For freeing the oxygen, the decomposing catalysts mentioned in the specification of application Serial No. 594,304, such as catalases, blood powder, metal compounds, may be employed. A very uniform evolution of gas and distribution of bubbles throughout the mass is obtained, as has further been found, if the oxygen is set free by substances which are capable of acting chemically on hydrogen peroxide and the like, for example substances such as chloride of lime, sodium hypochlorite and the like. By this means it is possible to influence in a most favourable manner the duration of gas evolution, and the number and size of the bubbles as desired.

It has also been found that the evolution of gas, namely with respect to the number and size of the gas bubbles, can be influenced to a large extent by the addition of suitable media, for example media which are capable of influencing the speed of decomposition and/or varying the surface tension. For this purpose soap solution, for example, has been found to be particularly suitable. The concentration of the soap solution may be so small that it does not act as a producer of froth. Other substances by which the number and size of the bubbles can be advantageously influenced are for example saponin, albumen, gum arabic, colloidal earths and the like.

By means of these additional substances, a tendency towards an increase in the number of the gas bubbles and a reduction in the size of the individual bubbles can be produced, and, further, a stabilizing action is exerted on the gas bubbles in the mass.

Finally, it has also proved advantageous to take care that small amounts of alkali or ammonia are present.

A further method of producing the hollow spaces interspersed throughout the grinding body is to incorporate in the mass from which the grinding body is manufactured substances which, after partial or complete solidification of the grinding body, be again removed by measures such as'solution, fusion, evaporation and the like. Thus, for example, there may be uniformly incorporated in the mixture of abrasive material and binding medium balls of sugar, soluble salts and the like, which balls may be again dissolved out after the mass has solidified by a suitable solvent, such as water, or there may be incorporated in the mass balls consisting of naphthalene or similar substances which are then removed from the solidified body by fusion or evaporation.

An important method according to the invention is first to fill a mould with the balls and then to fill the intervening spaces between the balls, for example by introducing a fluid mixture of abrasive material and binding agent, and then to solidify the mass. After dissolving out the balls, grinding bodies in which the hollow spaces have connecting openings at the places at which the balls were in contact then remain. By this means the solution, fusing-out or evaporation of the balls is facilitated and on the other hand a favourable influence is exerted towards keeping cool during the grinding operation the grinding discs manufactured in this manner.

Two forms of wheel produced according to the process of my invention are disclosed in the accompanying drawing, in which:

Fig. 1 is a cross section through a wheel substantially along the line 11 of Fig. 2.

Fig. 2 is a cross section along the line 22 of Fig. 1.

Figs. 3 and 4 are cross sections respectively along the lines 3-3 of Fig. 4 and 44 of Fig. 3 showing a modified form of wheel.

The grinding bodiesmanufactured in accordance with the invention can be completely interspersed by artificially produced hollow spaces.

For example, as shown in Fig. 1, we provide a body 2 having hollow spaces or pores 4 and a central opening 6. The walls between the pores are formed of binding material and particles 8 of abrasive. The grinding bodies can also be so formed, for example, that certain parts have the desired cellular structure owing to the interspersion with hollow spaces, while other parts are solid. Thus, for example, the grinding bodies in accordance with the invention can be manufactured in such a manner, as shown in Figs. 3 and 4, that the core 10 surrounding the axis is solid, in which case the solid portion may have a certain natural porosity, whereas the annular zone (working zone) surrounding the solid core portion may have a cellular structure in accordance with the invention, consisting of pores 4 and walls including abrasive particles 8. In this case the requirement that the total volume of the hollow spaces must equal at least 50% of the volume of the totalmass holds good, of course,

only for the part of thegrinding body which is Example 1 A mixture of 140 grams of corundum powder No. (i. e. sifted through a sieve with 80 times 80 meshes per square inch) 60 grams of a clayey binding material and 0.1 gram aluminum powder is made into a dough with 60 cc. of water. After 10 cc. of a 2.5% glue solution have been added 5 cc. of a 5% sodium hydrate solution are stirred in. The homogeneouspaste is transferred into a mould, where the development of the gas begins and the paste starts rising. After the formed mass has been dried to some extent it is transferred to an oven and fired properly..

Example 2 The two mixtures a and b are firstly prepared separately.

Mixture a: 30 grams of clay, so called Klingenberger, are mixed with 3.5 grams of finely ground chalky sand in a dry state after the latter has been prepared previously by coating it with 20 cubic centimeters of a 5% paraffin solution in benzol. The mixture is agitated with 40 cc. of water. Afterwards 70 grams of corundum No. 80 (sifted through a sieve with 80x80 meshes per square inch) are introduced into the paste.

For the preparation of mixture b 30 grams of Klingenberg clay are mixed with 25 cubic centimeters of water and 10 cubic centimeters of a 2.5% solution of glue in water. Then 2 cc. of concentrated hydrochloric acid solution are added. Finally 70 grams of corundum No. 80 are stirred in.

Both mixtures a and b are then speedily mixed with each other and transferred to a mould. The development of the gas starts nearly immediately. After the paste has stopped rising the mould is removed the mass dried and then fired in suitable kilns.

Ezample 3 Into 2 kilograms glue solution (prepared from 2 parts by weight of glue and 3 parts B. W. of water) cubic centimeters of hydrogen peroxide (30% H202) are added at a slightly elevated temperature. 5 kilograms of a powdered lead glass which have been moistened with 750 cc. of water are then introduced with agitation. After about 25 grams of manganese dioxide, MnO-z have been added, which were previously suspended in 250 cc. of water the development of the gas begins in the course of which 5 kilograms of abrasive material such as silicium carbide, ground corundum or the like are added. The mass which is still warm is filled into moulds, dried and fired subsequently till the binding material sinters.

Example 4 To grams of waterglass (36 B.) are added 10 cc. of water with 5 cc. of hydrogen peroxide (30% H202). Into the solution 600 grams of powdered silicium carbide Nr. 30 (sifted through a sieve with 30x30 meshes per square inch) are introduced. When the paste is homogeneous a suspension of 2 grams of manganese dioxide in 5 cc. of waterglass of 36 B. is added and mixed thoroughly. The mass is then put into .moulds. After suitable drying the moulded apertured bodies may be impregnated in order to strengthen them with a solution of for instance an artificial resinous substance such as is known under the trade name bakelite as solvent being used for instance acetone. As soon as the bodies are dry they may be heated, preferably under pressure, to about 150 to C.

Example 5 300 grams of a clayey binder are mixed with 1000 grams of silicium carbide No. 80 (sifted through a. sieve with, 80x80 meshes per square inch) and stirred with 280 cc. of water and 50 cc. of a 2.5% glue solution. To the paste are added 7 cc. of hydrogen peroxide solution (30% H202) and a suspension of 0.5gram manganese dioxide in 5 cc. of water. The paste is put into moulds and, after the development of gas has ceased, dried whereupon the bodies are fired in suitable kilns.

Example 6 330 grams silicium carbide No. 46 (sifted through a sieve with 46x46 meshes per square inch) are coated with about grams bakelite", by impregnating the grains with a suitable Bakelite solution in acetone drying and sieving. An annular mould of 160 mm. diameter is filled with 500 grams sugar pearls of 4 mm. diameter and the intervening spaces between the sugar pearls are carefully filled with the prepared grains. The mould which is thus filled is heated to 150 for about 2 hours after which its solidified content is taken out and cooled. The sugar pearls are now dissolved out with hot water, the disc is dried and saturated with liquid bakelite and then hardened in known manner. The volume of the hollow spaces with which the grinding body is interspersed is about 3350 times the volume of the abrasive grains employed.

We claim:

1. Method of manufacturing grinding bodies comprising incorporating in a plastic mixture of abrasive material and binding medium substances containing active oxygen, and adding substances which, like chloride of lime, are capable of acting chemically on the substances containing the active oxygen, thereby generating oxygen bubbles before the mass solidifies in such number and size as toproduce a body of cellular structure in which the total volume of the hollow spaces present amounts to 50 to of the grinding body interspersed with hollow spaces, and the hollow spaces are larger in size than the grains of abrasive material present.

2. Method of manufacturing grinding bodies comprising incorporating in a plastic mixture of abrasive material and binding medium substances which are capable of generating gas bubbles and substances which, like soap water, are capable of influencing the number and size of the gas bubbles generated, and generating gas bubbles from these substances before the mass solidifies in such number and size as to produce a body of cellular structure in which the total volume of the hollow spaces present amounts to 50 to 80% of the grinding body interspersed with hollow spaces, and the hollow spaces are larger in size than the grains of abrasive material present.

3. Method of manufacturing grinding bodies comprising incorporating in a plastic mixture of abrasive' material and binding medium substances which are capable of generating gas bubbles and substances which, like soap water are capable of influencing the number and size of the gas bubbles generated and small quantities of alkaline substances, and generating gas bubbles from these substances before the mass solidifies in such number and size as to produce a body of cellular structure in which the total volume of the hollow spaces present amounts to 50 to 80% of the grinding body interspersed with hollow spaces, and the hollow spaces are larger in size than the grains of abrasive material present.

4. Method of manufacturing grinding bodies comprising incorporating, in a plastic mixture of abrasive material and binding medium, hydrogen peroxide, adding hypochlorite and a dilute soap solution to the mixture, and thereby generating gas bubbles before the mass solidifies in such number and size 'as to produce a body of cellular structure in which the total volume of the hollow spaces present amounts to 50 to 80% of the grinding body interspersedwith hollow spaces, and the hollow spaces are larger in size than the grains of abrasive material present.

5. A method of producing an abrasive compound having artificial porosity which comprises forming a plastic mixture of abrading and binding materials, of a material which will liberate gas, and of materials which are capable of efiecting and regulating the gas development of said gas liberating material, causing said gas liberating material to release gas to form hollow spaces in the mass, said hollow spaces being interspersed evenly throughout the mass and'being of a size larger than the grains of the grinding material employed.

6. A method of producingan abrasive compound having artificial porosity which comprises forming a plastic mixture of abrading and binding materialsof a material which will liberate gas, and of an aqueous solution of soap, causing V material used.

THEODOR POHL. JOSEF SCHNEIDER. 

